This invention relates to a tamper-proof seatbelt system for a motor vehicle and, more particularly, to a tamper-proof electrical circuit for use in association with retractable seatbelts designed to restrain and protect vehicle occupants.
It has been statistically demonstrated that seatbelt restraint systems for motor vehicles when properly used substantially reduce the risk of injury to vehicle occupants. In spite of this, motorists have been reluctant to use seatbelts. In order to encourage the use of seatbelts, motor vehicles built in the United States are now equipped with warning buzzers and warning lights to remind vehicle occupants to fasten their seatbelts. In the future, vehicles will not only be equipped with warning buzzers and warning lights, but also will be equipped with ignition interlock systems which will prevent the engine of the motor vehicle from being started if seatbelts are not fastened.
The typical ignition interlock seatbelt system of the prior art employs for each setting position a first switching device for sensing whether or not the seatbelt is in a retracted or in an extended position and a second switching device, usually a load sensing switch built into the seat, for sensing whether or not the seating position is occupied. An electrical relay or the like having a switching contact in the vehicle's ignition starting circuit is connected with the first and second switching devices. Failure to extend or buckle the seatbelt corresponding to a given occupied seating position energizes the relay and prevents the vehicle's engine from being started. Also, a buzzer and/or warning light may be energized simutaneously. In this prior art system, there is nothing to prevent a vehicle occupant from defeating the ignition interlock system by fastening his seatbelt behind him or by otherwise tampering with the electrical circuit by physically removing, short-circuiting, or cutting the lead wires of the warning devices, sensing switches, and ignition-circuit relay contact.